Studies of FMR1 KO mice have identified discrete alterations in synaptic plasticity in specific brain regions, including an increase in long-term depression (LTD) in the hippocampus,23,29 and preclinical data suggest that reducing LTD in FMR1 KO mice requires activation of endocannabinoid receptors.19 Therefore, it is hypothesized that CBD may increase synaptic plasticity in FXS, facilitating one of the basic cellular mechanisms thought to be associated with learning and improvements in cognition.29 Here, FMR1 is linked to fragile X syndrome.